This application claims the benefit of Korean Patent Application No. 2002-26490 filed on May 14, 2002 and Korean Patent Application No. 2002-55697 filed on Sep. 13, 2002, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by references.
(a) Field of the Invention
The present invention relates to a cathode ray tube. More particularly, the present invention relates to a cathode ray tube having a color selection apparatus realized by a shadow mask that includes a plurality of apertures separating electron beams and a mask frame that supports the shadow mask.
(b) Description of the Related Art
A cathode ray tube (CRT) is generally a display device in which three electron beams emitted from an electron gun scan a phosphor screen to realize predetermined images. A color selection apparatus is provided within a tube and at a position adjacent to the phosphor screen. The color selection apparatus includes a shadow mask and a mask frame, and acts to separate the three electron beams so that the electron beams land correctly on red (R), green (G), and blue (B) phosphor layers of the phosphor screen.
With the typical shadow mask, that is, the typical dome-shaped shadow mask as opposed to the aperture grill type shadow mask, apertures are formed by an etching process. Non-etched areas between the apertures in a vertical direction of the screen are referred to as bridges, and predetermined portions of the electron beams are blocked by the bridges during the scanning process.
Accordingly, an alternating dark and bright pattern appears on the CRT screen, resulting in the occurrence of a moire phenomenon when such patterns are viewed by users. The moire phenomenon occurs according to a moire wavelength and a moire intensity. Typically, the moire wavelength is generated by interference from the cyclical repetition of the bridges and a wavelength of scanning lines, while moire intensity depends mainly on a size of the electron beams and a length of the bridges.
The moire intensity measurement is proportional to a density of electron beams passing through the shadow mask and a density of electron beams blocked by the bridges. Accordingly, in order to reduce moire intensity, the size of the electron beams must be reduced, a structure of a deflection apparatus or of an electron gun must be altered, and/or the shape and size of the apertures must be adjusted, etc.
U.S. Pat. Nos. 5,378,959, 5,619,094, and 5,525,858 disclose configurations to minimize the moire phenomenon.
During operation of CRTs, picture distortion becomes greater as the electron beams are deflected toward the peripheries of the screen. The electron beams that are deflected to horizontal edges of the screen experience an increase in their horizontal diameters and a reduction in their vertical diameters. This results in the vertical diameters of the electron beams landing on the horizontal edges of the screen being reduced to approximately 70% of the vertical diameters of the electron beams landing at the center of the screen.
Such a reduction in the vertical diameters of the electron beams results in an increase in the moire intensity at the horizontal edges of the screen such that moire patterns are formed at these areas of the screen as shown in FIG. 8 (the areas of the screen where the moire patterns are formed are indicated by the diagonal lines).
The moire patterns may be reduced by using a moire compensation circuit. However, when there is a high moire intensity, a moire pattern remains even with the operation of the moire compensation circuit resulting in the deterioration of screen characteristics. A variable focus voltage of the electron gun may be adjusted to increase the vertical diameter of the electron beams at horizontal edges of the screen to decrease distortion, however, doing so decreases focus characteristics of the electron beams.
Therefore, a vertical pitch of the apertures and a length of the bridges must be carefully selected to correspond to variations in vertical beam diameters of the electron beams to reduce moire intensity. However, since the vertical pitch of the apertures and the length of the bridges are closely related to the structural strength of the shadow mask and the tolerance of the screen, such choices in the dimensions of the apertures and bridges must be made with great care.
In one aspect, the present invention provides a cathode ray tube with a color selection apparatus that inhibits an increase in moire intensity caused by a reduction in a vertical diameter of electron beams, thereby preventing the occurrence of a moire phenomenon at peripheral portions of a screen to ultimately result in an improvement in picture quality.
In one embodiment, a cathode ray tube includes a tube realized through a face panel on an inner surface of which a phosphor screen is formed, a funnel is connected to the face panel, and a neck is connected to the funnel. A color selection apparatus includes a shadow mask having a plurality of apertures formed in an effective area of the shadow mask for the passage of electron beams and a mask frame mounted to an inside of the face panel while fixedly supporting the shadow mask. An electron gun is mounted within the neck and emitting three electron beams toward the phosphor screen. A deflection apparatus is mounted to an outer circumference of the funnel and generating a deflecting magnetic field in a path of the electron beams to deflect the electron beams. A moire compensation circuit is included in a circuit portion connected to the deflection apparatus, the moire compensation circuit causing interference in a deflecting signal supplied to the deflection apparatus to perform moire compensation, wherein the color selection apparatus satisfies the following condition,   0.76  ≥      Ke    Ko    ≥  0.85
where Ko is a K value at a center point of the effective area and Ke is a K value at a horizontal end of the effective area; and
wherein K satisfies the following condition,   K  =            DL      Pv        xc3x97          Bs      Ps      
where DL is a vertical length of the apertures, Pv is a vertical pitch of the apertures, Bs is vertical diameter of the electron beams landing on the effective area, and Ps is a vertical pitch of the electron beams landing on the effective area.
According to another aspect, a cathode ray tube with the color selection apparatus includes a tube realized through a face panel on an inner surface of which a phosphor screen is formed, a funnel is connected to the face panel, and a neck is connected to the funnel. A color selection apparatus includes a shadow mask having a plurality of apertures formed in an effective area of the shadow mask for the passage of electron beams and a mask frame mounted to an inside of the face panel while fixedly supporting the shadow mask. An electron gun mounted within the neck emits three electron beams toward the phosphor screen. A deflection apparatus mounted to an outer circumference of the funnel generates a deflecting magnetic field in a path of the electron beams to deflect the electron beams, wherein the color selection apparatus satisfies the following condition:   0.80  ≥      Ke    Ko    ≥  0.85
where Ko is a K value at a center point of the effective area and Ke is a K value at a horizontal end of the effective area, and
wherein K satisfies the following condition,   K  =            DL      Pv        xc3x97          Bs      Ps      
where DL is a vertical length of the apertures, Pv is a vertical pitch of the apertures, Bs is vertical diameter of the electron beams landing on the effective area, and Ps is a vertical pitch of the electron beams landing on the effective area.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.